Ionic Liquid-Chelated Prussian Blue Crystals for Sodium-Ion Batteries: Synthesis, Characterization, and Electrochemical Performance

Prussian blue (PB) and its analogs have attracted attention in sodium-ion batteries due to their high theoretical capacity and good electrochemical stability. However, their crystal structure instability and low charge transfer efficiency limit their performance in high-rate and long-cycle applications. In this study, ionic liquid [EMIM][BF4] was introduced as a chelating agent to optimize the electrochemical properties of PB. Results show that an appropriate amount of [EMIM][BF4] significantly improves the crystallinity of PB, reduces crystal defects, enhances dispersion, and promotes the Fe3+/Fe2+ redox reaction via coordination, thereby improving the conductivity and charge transfer efficiency of the electrode material. Electrochemical tests reveal that the PB-L5 sample maintains a high specific capacity and low charge transfer resistance at a high current density of 500 mA g–1, exhibiting excellent rate performance and cycling stability. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) further confirm the positive impact of [EMIM][BF4] on battery performance. Overall, this study presents a new strategy for enhancing the performance of Prussian blue electrode materials, demonstrating that appropriate ionic liquid modification can effectively improve electrochemical performance, offering potential applications in sodium-ion batteries and other energy storage systems.